This invention relates to a monitor for use in a vehicle to check the operation of an oxygen sensor.
Three-way catalytic converters used on automotive engines are the most commonly used method for meeting the emissions requirements established by the regulations set forth in the Clean Air Act of Dec. 31, 1970 in the U.S. When a closed loop system having a catalytic converter is used, an oxygen sensor is located in the exhaust manifold to provide a feedback signal to an electronic control unit. The electronic control unit maintains the engine input air to fuel ratio as near stoichiometry as possible for peak catalytic converter efficiency by measuring the oxygen type content in the exhaust gas. Both galvanic oxygen sensor (zirconia) of the type disclosed in U.S. Pat. Nos. 3,835,012, 4,107,018, 4,147,513, 4,377,801 and 4,387,359 and resistive (titania) oxygen sensors of the type disclosed in U.S. Pat. No. 4,007,435 have been evaluated as a way to measure the oxygen content in an exhaust gas.
In all of the prior art sensors some efforts have been made to reduce the effect of exhaust gas on the sensor element, such as by applying a coating on the sensor element or providing baffles in order to prevent the direct contact of the exhaust gas with the sensor element. However, after an extended period of use, particles of materials carried by the exhaust gas can be deposited on the sensor element and/or a chemical reaction may occur with the exhaust gases that can result in the generation of incorrect feedback signals.
It is anticipated that in the future it may be necessary to check the operation of the oxygen sensors as part of good maintenance practices as often as every ten thousand (10,000) miles.